Should I ask for a poly?

I've been lurking for a long while but figured I would finally join. I've been married for around 10 years. Probably about 3 years ago I started noticing my wife's behavior changing. She said it was work related stress. She started staying late at work. Maybe two hours late on most nights. She was always in a bad mood and we began to have lots of little fights. She began to work out to lose some weight. Our sex life struggled. I would only see her in her granny panties but after work once (that I saw) she changed out of very cute underwear. One time when she was really drunk she said that she knew we would get a divorce some day. I began to suspect something. There are some other red flags, but I was never able to find anything definitive to prove cheating. She has worked with a man for ten years that she has become very close with. They both started in very junior positions and have excelled and are now in positions of leadership in her company. Their offices are literally right next to each other so they spend a lot of time together. They have had a few work trips together including overnight stays at hotels. Like many I confronted her without any real evidence. There was some questionable credit card charges that turned out to be a duplicate charge of a previous hotel stay for our anniversary. She reacted unexpectedly. As soon as I asked if she was having an affair she started crying. She said no and asked why I thought so and I told her about the charges. She said she didn't stay at the hotel and called and the credit card removed the fee. Since then we have had ups and downs. I began snooping but I was never able to find much. She isn't glued to her cell phone. She has in the last year or so stopped working late. At annual company Christmas party we no longer sit next to OM or OMW. (Previously we would always sit with them). She seems like overall she is happy. Meanwhile I have really struggled the last few years. I think about her possible affair every single day. I have had countless sleepless nights. It has consumed me. I've been working on myself (NMMNG and MMSL) which has helped, but I know I have a long way to go. At one point we did HNHN, but she wasn't really into it. She very reluctantly read the book and it was a hassle getting her to fill out the emotional needs questionnaire. I didn't see her put much of an effort into meeting my needs. I have tried, but I still have a long ways to go. So at this point I would like your opinions regarding asking her to take a poly. I would feel like a terrible husband asking for one if she has not cheated, but my gut has continued to scream that something happened. I know that they are not perfect but I don't know how much move of this I can take.

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